As to proximity sensors detecting that a human body has approached an arbitrary target object, there exist various ones depending on the detection method thereof.
In human detection sensors that use light such as infrared rays, a prescribed “window” is necessary for a light receiving element to receive thermal infrared rays emitted from a human body, or to irradiate a human body with infrared rays from an infrared light emitting diode and receive the reflected light.
On the other hand, a human detection sensor that detects the change in electrostatic capacitance, which is recently used widely for smart phones etc., has an extremely short detection distance.